This present invention relates generally to a method for forming a molded surface and, more particularly, to a method for creating a substantially defect free and bubble free molded surface on the outmold side of a casting or other surface using thermosetting resin systems.
In the thermoset casting industry, a thermosetting resin is poured into a mold of desired configuration, or applied to a substrate, and then allowed to cure. After sufficient curing time, the cured product is removed from the mold or substrate for further use or processing. The surface portion of the cured product which is in contact with the mold or substrate is referred to as the "inmold" side, whereas the surface portion of the product opposite the mold or substrate surface is referred to as the "outmold" side. Standard casting methods predominantly use the inmold side of the product as the "good" or finished side of the product. This is because the inmold side conforms to the mold or substrate surface and can be provided with an desired patten or surface texture, thus resulting in a substantially finished surface. In contrast, the outmold side of the product is open to ambient conditions as it cures and thus has neither the functional nor aesthetic qualities of the inmold side.
In a typical inmold casting method designed to use the inmold side, a mold or substrate surface is prepared by waxing and polishing. Following this preparation, a thin coat of resin referred to as a gel coat is sprayed or otherwise applied onto the mold or substrate surface. A matrix of thermosetting resins and various inorganic fillers is then poured, sprayed or otherwise applied into the mold or onto the substrate. The thermosetting resin bonds to the gel coat. After sufficient curing time, the entire molded part is removed from the mold or substrate. In the above process, the inmold surface of the article is essentially in finished form, whereas the outmold surface is generally pitted, flawed and irregular.
A limited number of outmold casting techniques are known in the prior art. On such outmold casting technique is described in U.S. Pat. No. 3,341,396 issued to E. M. Iverson. In this patent, a pigmented base layer of a resin material is applied to a substrate, after which a base layer having a color pigment is applied to the base layer. This is followed by application of a transparent coating on top of the pigmented layer. Flow and diffusion of the pigmented layer is then induced by movement of a tool through the transparent layer. In a further outmold method described in U.S. Pat. No. 5,055,324 issued to Stecker, a resin system is poured onto a substrate. In the above described outmold casting methods, the top or outmold side of the article is generally pitted, flawed and irregular. Thus, such surfaces require significant sanding and polishing to create an acceptable finished surface.
Limitations exist with respect to both inmold and outmold casting techniques. A principal advantage of an inmold system is that the inmold surface of the molded article is essentially finished in final form as it is removed from the mold or substrate. The ability to create pigmented patterns within the molded article is, however, limited. A principal advantage of an outmold casting method is the ability to create different and desirable pigment patterns in the molded article either by inducing physical motion as described in Iverson U.S. Pat. No. 3,341,396 or by inducing controlled diffusion of pigment as described in Stecker U.S. Pat. No. 5,055,324. A disadvantage of conventional outmold casting processes is that the outmold surface is pitted and flawed. Thus, the surface must be accepted complete with flaws and imperfections or must be sanded and polished in order to fully finish the surface. Such a step can be expensive and time-consuming.
Another alternative is to utilize injection molding in a closed mold. Injection molding techniques are often limited to thicker articles inasmuch as the cross-section of the article is reduced, the tendency to develop unsightly swirls and patterns is increased.
Accordingly, there is a need in the art for a method to create a substantially finished molded surface which substantially eliminates any sanding, polishing or further finishing.